Synthetic woods formed of a resin foam covered with a dense outer layer have been widely used for indoor applications, including wet areas, furniture, and interior finishes, for their advantages such as dimensional stability, uniform mechanical strength, uniform surface conditions, and durability. In contrast to natural wood, the synthetic woods exhibit no water absorbency and have uniform material quality and resistance to rot due to rot fungi, contamination due to mold, and damage due to infestation of insects such as termites.
The synthetic woods are designed to have similar density and machinability in nailing and sawing, for example, to those of natural wood because synthetic woods that can be handled in the same manner as natural wood are desired. On the other hand, the synthetic woods are designed to have low weight, excellent machinability, and high surface strength. Such synthetic woods are produced by covering a body formed of a resin foam with a skin layer or by bonding a highly adhesive outer layer formed of an unfoamed resin or a low-expansion resin foam to a body formed of a resin foam to prevent damage due to external forces.
Recycling of materials has been actively promoted with increasing need for reduction of waste in the plastics industry. Use of waste resin as a source material for synthetic wood has been attempted because enormous amounts of waste resin have been produced, particularly polystyrene (hereinafter referred to as PS) and polypropylene (hereinafter referred to as PP), which have been manufactured in large amounts.
PS and PP, however, are difficult to use outdoors because of their poor weather resistance and thus have limited applications. The problem of poor weather resistance remains even if high-impact polystyrene (hereinafter referred to as HI-PS) is optionally added to PS.
To enable the use of such resins outdoors, studies have been conducted on a weather-resistant synthetic wood including a body formed of PS or PP and covered with an outer layer formed of a weather-resistant resin such as an acrylonitrile-acrylic rubber-styrene copolymer (hereinafter referred to as AAS) and an acrylonitrile-ethylene propylene rubber-styrene copolymer (hereinafter referred to as AES). Unfortunately, these resins have poor adhesion to a foam of PS or a mixture of PS and HI-PS and are thus easily peeled from the foam at the contact surface therebetween.